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OCR Maths Core 3 question!

http://pdf.ocr.org.uk/download/pp_08_jun/ocr_30881_pp_08_jun_l_gce_4723.pdf?

The very very last question please 9iii) where it says show that the gradient is -1

i'm up to the point where i've got x^4-5x^2+100=0

but what do I do from there?

Reply 1

Allofthem

Try substituting x^2 for u, the rest ought to become clear.

Reply 2

Dijipo

Set dy/dx as -1 and then move that over to the other side to make dy/dx=0. Then work out the discriminant and it should be negative - meaning no real roots.

And btw - its asking you to show the gradient is NEVER -1